Issue 42

G. Bolzon et alii, Frattura ed Integrità Strutturale, 42 (2017) 328-336; DOI: 10.3221/IGF-ESIS.42.34

discontinuity generated by the crack opening. The visual superposition of the digital image and of the reconstructed field avoids any misinterpretation of the results. A characteristic feature of the tests performed on thin metal foils is the appearance of wrinkles ahead of the fracture zone, see the bright strips in Fig. 2 . 3D DIC permits to reconstruct the out-of-plane displacement distribution, represented in Fig. 4 in correspondence of four different loading steps. The fractured edges undergo the largest deflection from planarity but the foil corrugates in the ligament region as well, as shown by the measurements reported in Fig. 5. Notice that the mean out-of-plane displacement is almost null all along the test, while the maximum values increase significantly in the softening regime, i.e. starting from about 1 mm relative displacement, see Fig. 5(a) and Fig. 6(a). On the contrary, the depth of the wrinkles developing in the ligament increases almost monotonically with the load up to the peak of the reaction force, and then reduces. The almost symmetric fracture propagation during the test is confirmed by the graphs in Fig. 6(b), visualizing the crack growth as the overall displacement increases. The crack length is evaluated as the distance between the current and the initial position of the relevant tip.

Figure 2 : Snapshot sequence during the test, in the initial configuration (a) and at overall displacement 0.5 mm (b) , 0.75 mm (c) and 1 mm (d) .

Figure 3 : Strain component along the loading direction at 1 mm overall displacement.

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